After trying to change the A records (I don't know much about hosting) I realized that I'm having this same issue. The Cpanel error is happening to me too. Please restore glennaallen.x10host.com as well. It's much appreciated. Thank you.
It's the same situation. I'm using godaddy and recently purchased a new domain. I changed the nameservers for the new domain to be ns1 and ns2....(what they say to use). I try to add it as an Addon domain and get the same error message. I'm guessing there is a glitch with x10?